Semi-dispenser cathode with overlying emissive coating



June 20, 1967 D. SCHWENDER 3,327,158

SEMI '-DI SPENS ER CATHQDE. WITH QVERIJY'HQG EMI S S IVE COAT ING Filed June 26, 1963 I N VE N TOR l 0nard .D Schulz/Ida! BY MMM ATTORNEY 3,327,158 SEMI-DISPENSER CATHODE WITH OVERLYING EMISSIVE COATlNG Leonard D. Schwender, Sylvan Heights, Pa., assignor to Syh'ania Electric Products Inc., a corporation of Delaware Filed June 26, 1963, Ser. No. 292,195 3 Claims. (Cl. 313-346) This invention relates to electrodes for electron discharge devices and more particularly to cathodes and their fabrication.

A cathode for an electron discharge device and particularly an electron tube is frequently a metal cylinder with a layer of electron emissive material thereon. One of the most common processes for making cathodes is to select a metal alloy strip, form it into a cylindrical configuration, and spray or deposit in some manner a layer of potentially emissive material thereon to provide a cathode assembly. Following, the assembly is disposed in an electron discharge device and processed in a manner well known in the art to cause the activation of the emissive materials and provide an electron source, the cathode.

Such cathodes and fabrication processes have been vastly improved in accordance with the teaching of Kerstetter et al. in US. Patent 2,986,671 issued May 30, 1961. Herein, a self-supporting pliable film is provided wherein the potentially emissive materials are homogeneously dispersed in an organic binder. The film is cut to a desired configuration, adhered to the cathode base by wetting the base with a solvent for the film, and touching the film thereto whereupon the film wraps itself about the base to provide a cathode assembly. Subsequently, the assembly is disposed in an electron discharge device and processed to volatilize the organic binder and render the materials suspended therein emissive.

Although the above-mentioned cathodes and processes are extensively used in present-day electron tube manufacture and have provided previously unknown and unobtainable electrical characteristics, it has been found that there are some types of electron tubes and applications thereof wherein such cathodes are still not the ultimate. For example, the ever increasing demand for reduced electrode spacing, increased voltage gradient between electrodes, increased electron emission, and reduced arcing between electrodes in rectifier type tubes and particularly the so-called damper tubes in television sets are a constant problem with presently available cathodes.

Thus, it is an object of this invention to enhance the arcing and electron emission capabilities of a cathode adapted for use in an electron discharge device.

Another object of the invention is to increase the density and outermost surface smoothness of a cathode having an emissive material layer thereon and adapted for use in an electron discharge device.

Still another object of the invention is to provide a cathode having an emissive material layer thereon with an increased hardness and resistance to abrasion.

An additional object of the invention is to improve the bonding of the cathode emissive layer and the metal strip as well as the area of contact and conduction therebetween.

A further object of the invention is to improve the uniformity and reproducibility of a cathode emissive material layer fabrication process.

A still further object of the invention is to economically and automatively enhance the fabrication of cathodes having an emissive material layer of increased density and increased outermost surface smoothness.

Patented June 20, 1967 Briefly, these and other objects are provided by a structure having a metal base, a compacted layer of metal particles impregnated with emissive materials sintered thereto, and a densified layer of emissive materials with a smooth outermost surface thereon. This structure may be fabricated in accordance with one embodiment of the invention by adhering a self-supporting film containing potentially emissive materials suspended in an organic binder to a porous metal layer sintered to a metal strip, forcing a portion of the film into the porous metal layer, compacting the film and the porous metal layer, forming the resulting laminate into a desired configuration adapted for insertion into an electron discharge device, and heating the laminate to volatilize the binder in the film and decompose the potentially emissive materials.

For a better understanding of the present invention, together with other and further objects, advantages, and capabilities thereof, reference is made to the following disclosure and appended claims in connection with the accompanying drawing in which:

FIG. 1 is a photomicrograph of a cathode assembly prior to activation in an electron discharge device.

Referring to the illustrative microphotograph of a laminated structure, enlarged 600 times, there is shown a base metal strip 3, a compacted self-supporting film 7 containing potentially emissive materials homogeneously dispersed and suspended in an organic binder, and a densified layer 5 of impregnated potentially emissive material 9 and sintered metal particles 11.

As will be evident from the process hereinafter explained, the self-supporting film 7 has a hard and smooth outermost surface 13 and a density and thickness uniforrnity unobtaina'ble by ordinary means of fabrication. Further, the densified layer 5 containing the sintered metal particles 11 impregnated with potentially emissive material 9 and interconnecting the metal strip 3 and the self-supporting film 7 provides a transitional layer bonding the strip 3 and the film 7. Moreover, the compacted film 7 and densified layer 5 have a combined thickness of about 0.0005 to 0.003 inch and a density in the range of about 3.5 gms./cm. to 4.5 gms./cm.

It is well known that arcing and electron emission characteristics of electron tubes are of primary importance when the tube is subjected to high voltage conditions such as those prevalent in television set damper tube applications. It is also well known that the above characteristics are dependent upon a number of factors including the emissive layer capability initially and after extended use, the adherence of the emissive layer to the strip material, the uniformity and outermost surface condition of the emissive layer, and the ability to activate the emissive layer.

When the emissive layer is provided by a self-supporting film 7, the uniformity of thickness and emissive material dispersion as well 'as the smoothness of the outermost surface are, as far as is known, far in advance of other methods for providing a layer of coating. Alternately, the emissive layer may be provided by a cast film which is not self-supporting thereby permitting the use of a greatly reduced amount of binder content therein. Obviously, reduced amounts of binder are advantageous in cathodes adapted for use in electron discharge devices. When the film 7 is compacted, the outermost surface is further treated and any rough or uneven defects therein removed. The compacting of the film 7 produces a hardened and dense layer which is highly resistant to deformation and abrasion.

Additionally, the densified layer 5 of sintered metal particles 11 impregnated with emissive materials 9 not only bonds the film 7 to the base strip 3 but provides highly conductive heat and electrical paths therebetween.

When the metal particles 11 are dispensed onto the strip 3 by a casting process, the uniformity of thickness and porosity is believed to be unequaled. The compacting of the layer 5 after the emissive materials 9 have been impregnated therein forms an intimate contact therebetween. Moreover, the emissive material 9 in the layer 5 is gradually dispensed for an extended period of operation.

Thus, it is believed that arcing is greatly reduced and electron emission enhanced in tubes having a high voltage gradient between electrodes. Uniformity of thickness, density. emissive material dispersion, and outermost surface smoothness of the film 7 as well as hardness and resistance to deformation thereof are major contributing factors. The bonding of the film 7, electrical and heat conductive paths, intimate contact between metal and emissive particles, as well as the uniformity of thickness and porosity of the layer 5 also provide advantages previously unknown.

In the process of fabricating cathodes for electron discharge devices, a base metal 3 is selected which may be any of numerous materials normally used for cathode bases. For instance, tungsten, platinum, tantalum, and iron are frequently used cathode base materials and are applicable to the present process. Moreover, nickel and alloys and mixtures thereof are preferred materials when the potentially emissive materials used therewith are alkaline earth carbonates. Further, powdered metal particles in a size of about 1,u to 20 are selected to provide the sintered metal layer thereon.

The metal particles 11 initially are disposed upon and sintered to the cathode base metal 3 to provide a porous metal layer. Numerous processes for providing a sintered metal layer are available and a preferred process is to cast a film containing metal particles homogeneously dispersed in an organic binder. Then, the film is adhered to the metal base and the film and base are heated to volatilize the binder and sinter the particles to the base.

The film may be self-supporting or cast directly onto the metal base depending upon whether the process is continuous or a so-called batch process. This film casting process and advantages thereof such as thickness, uniformity, porosity control, and numerous other advantages are set forth in detail by Kerstetter and Montgomery in an application bearing Serial Number 105,891 filed April 27, 1961, now abandoned.

The above self-supporting films are preferably cast to a thickness of about 0.002 to 0.006 inch and after sintering provide a porous layer of metal particles of a thickness in the range of 0.001 to 0.005 inch. The porosity of the sintered layer is about 70% to 90% with a density in the range of 1.5 gms./cm. to 2.5 gms./cm.

The above-mentioned ranges of thickness, density, and porosity are preferred although films containing metal particles suspended in an organic binder have been cast outside of these ranges. Films cast to a thickness of less than .002 and below a, density of 1.5 gms./cm. have been found to require exceptional care and precision equipment in order to handle the film without rupture. Further, films having a porosity above 90% have been found to be deficient in bonding the self-supporting film 7 to the metal strip 3 and the heat and electrical conductive paths therebetween less than adequate.

When the film is cast to a thickness greater than .006 inch and above a density of 2.5 gms./cm. the pressure required to form a cathode configuration has been found excessive and detrimental to the film 7 thereon. Also, the films having a porosity of less than 60% require an excessive pressure to impregnate the film 7 into the densified layer 5.

Next, a self-supporting pliable film 7 containing the potentially emissive materials suspended in an organic binder is cast. Alternately, in a continuous process, the film may be cast directly onto the sintered metal particle layer. In either case, details of the films and casting process are readily available in the previously mentioned Patent Number 2,986,671 of Kerstetter et al.

Preferably, the potentially emissive materials 9 in the film 7 are alkaline earth carbonates such as co-precipitated barium, strontium, and calcium although metal particles may be included as disclosed by Lambert and McKiernan in their application filed April 27, 1961, bearing Serial Number 105,887. Self-supporting emissive films may be preferably cast to a thickness of about 0.0005 to 0.005 inch with a density in the range of approximately 0.5 gms./cm. to 1.7 gms./cm.

Films 7 cast thinner or less dense have been found to have inadequate emission capabilities while thicker and more dense films are difficult to adequately impregnate within the sintered metal particles layer and require excessive processing which is undersirable in electron tube manufacture.

Thereafter, the self-supporting pliable film 7 is adhered to the sintered metal layer by wetting the metal layer with a solvent for the film and contacting the film and metal layer as disclosed in the above patent. A preferred method is to merely hold the film in place by Wetting the edges thereof with distilled water. In this manner there is introduced a very minimum of materials which might possibly have a deleterious effect upon the emissive qualities of the cathode.

Thereafter, the metal base 3, sintered metal layer thereon, and self-supporting potentially emissive film 7 are subjected to sufficient pressure to cause a portion of the potentially emissive film to penetrate the sintered metal layer. Also, the pressure removes the excess water used to hold the film in place on the sintered layer. The pressure is preferably applied by a resilient pliable means to insure uniform penetration of the potentially emissive film into the metal particle layer.

Having caused a portion of the potentially emissive film 7 to penetrate the porous metal layer, the laminated structure is compacted in any one of numerous available techniques. For instance, when the structure is in the form of a laminated strip, a preferable method of compaction is to feed the strip through a series of rollers. Alternately, when the structure is of a form not adapted to rolling, compaction may be obtained by impact hammering. Obviously, most any method of compacting the structure is applicable and may be used in the process so long as the structure is densified and the outermost surface of the potentially emissive film is made smooth.

Subsequently, the structure, if not already in the desired form, may be shaped into a cathode configuration adapted for insertion into an electron discharge device. Thereafter, sufficient heat is supplied to activate the device and cause the organic constituents in the film to volatilize and the potentially emissive materials to be reduced to emissive materials which are in condition to function as an electron source or cathode.

As a specific illustration, a strip of nickel material about 0.0025 inch thick normally used for cathode bases had adhered thereto a self-supporting film containing nickel particles suspended in an organic binder. The film had a thickness of about 0.0035 inch and the nickel particles were in the range of about 3 to 9p. in size. The film was adhered to the nickel strip by wetting the strip with a solvent for the binder in the film and touching the film there- Next, the film and strip were fired at a temperature of approximately 1100 C. in a dissociated ammonia atmosphere having a dew point of about 40 C. to 50 C. Thereupon, the binder was volatilized and the metal particles sintered to the metal strip to provide a layer thereon having a thickness of about 0.0025 inch and a porosity of about Further, the sintered layer had a density of about 1.93 gms./cm.

Following, a self-supporting film containing alkaline earth carbonates suspended in an organic binder was cast to a thickness of about 0.0012 inch with a density of approximately 0.85 gm./cm. This film was adhered to and held in place on the sintered particle layer by dispensing distilled water along the edges of the film.

Thereafter, the laminate consisting of the metal base 3, porous sintered layer, and potentially emissive film 7 was rolled with sufiicient pressure to cause a portion of the film to penetrate the porous sintered layer and the excess water to be removed from the structure. Then the rolling pressure was increased sufliciently to compact and density the sintered metal layer with impregnated emissive materials therein and the potentially emissive film.

At this stage the potentially emissive film has a very hard and very smooth outermost surface and is bonded tightly to the impregnated metal particle layer which is sintered to the nickel strip. Moreover, the density of the impregnated metal particle layer and the potentially emissive film has been increased and the thickness thereof reduced. In this example the combined thickness of the impregnated metal layer and the emissive film layer was about 0.0018 inch with a combined density of about 3.94 gms./cm.

Subsequently, this laminate consisting of a metal base 3, an impregnated metal layer 5, and a potentially emissive film 7 was formed into a cylindrical cathode sleeve without damage to the outermost surface of the emissive film, disposed in a damper-type electron tube and activated in a manner ordinarily used in producing electron tubes. The resultant tubes exhibited electrical characteristics which, as far as is known, are unobtainable by other known techniques.

Thus, there has been provided a cathode fabrication process and cathode which has emission capabilities and a resistance to electrical arcing believed to be far greater than previously known cathodes. Moreover, the outermost surface of the cathode has a smoothness and hardness previously unknown. Further, the density of the emissive material layer and the impregnated sintered metal layer as well as the bonding therebetween and to the base metal strip provides advantages previously unobtainable. Additionally, the presented cathode fabrication process is easily automated and economical in that the cathode base and emissive layer thereon need no longer be made in separate and distinct operations but are combinable into a continuous process.

While there have been shown and described what are at present considered the preferred embodiments of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention as defined by the appended claims.

What is claimed is:

1. A cathode comprising a compacted laminate formed for deposition in an electron discharge device, said laminate having a metal base, an emissive material layer formed from a self-supporting film containing potentially emissive materials suspended in an organic binder from which the binder has been removed and the materials rendered emissive, and an interconnecting layer of metal particles impregnated with emissive materials, said interconnecting layer and said emissive material layer being of compacted form, said interconnecting layer being bonded to said emissive material layer and at least a portion of the metal particles therein sintered to said base, and said emissive material layer having a smooth and hard outermost surface.

2. The cathode of claim 1 wherein said emissive material layer is formed from a self-supporting film having a thickness in the range of about 0.0005 to 0.005 inch with a density in the range of about 0.5 to 1.7 gms./cm. and containing potentially emissive materials suspended in an organic binder from which the binder has been removed and the materials rendered emissive.

3. The cathode of claim 1 wherein said interconnecting layer is formed from a film of sintered metal particles having a thickness in the range of about 0.001 to 0.005 inch and a porosity in the range of about to percent.

References Cited UNITED STATES PATENTS 2,660,547 11/ 1953 Robertshaw 313-346 2,858,470 10/1958 Thurber 313-346 2,874,077 2/1959 Joseph et al 313-346 X 2,986,671 5/1961 Kersetter et al. 313-346 2,996,795 8/1961 Stout 313-346 3,041,209 6/1962 Beggs 313-346 3,110,081 11/1963 Hendriks 313-346 3,197,847 8/1965 Kerstetter 313-346 3,212,959 10/1965 Varadi et al 313-346 X 3,257,703 6/1966 Coad et al 313-346 X FOREIGN PATENTS 1,380,944 10/ 1964 France.

JOHN W. HUCKERT, Primary Examiner. A. J. JAMES, Assistant Examiner. 

1. A CATHODE COMPRISING A COMPACTED LAMINATED FORMED FOR DEPOSITION IN AN ELECTRON DISCHARGE DEVICE, SAID LAMINATE HAVING METAL BASE, AN EMISSIVE MATERIAL LAYER FORMED FROM A SELF-SUPPORTING FILM CONTAINING POTENTIALLY EMISSIVE MATERIALS SUSPENDED IN AN ORGANIC BINDER FROM WHICH THE BINDER HAS BEEN REMOVED AND THE MATERIALS RENDERED EMISSIVE, AND AN INTERCONNECTING LAYER OF METAL PARTICLES IMPREGNATED WITH EMISSIVE MATERIALS, SAID INTERCONNECTING LAYER AND SAID EMISSIVE MATERIAL LAYER BEING 